Timer and control mechanism



TIMER AND CONTROL MECHANISM Filed March 11, 1949 2 SheetsSheet l VINVENTOR. 1 262 M 44 2 K. M. KlEL 2,664,755

Jan. 5, 1954 K. M. KIEL 2,664,755

TIMER AND CONTROL MECHANISM Filed March '11, 1949 2 Sheets-Sheet 2 IINVEN TOR. I 'We/HW Z W7 #ZLEZ i'L/ BY Patented Jan. 5, 1954 TIMER ANDCONTROL MECHANISM Kenneth M. Kiel, Ann Arbor, Mich, assignor toKing-Seeley Corporation, Ann Arbor, Mich., a

corporation of Michigan Application March 11, 1949, Serial No. 80,861

6 Claims.

This invention relates to control mechanisms and, in particular, refersto mechanisms that may be both manually and automatically operated.

A specific usage of control mechanisms of the general type hereindescribed is in automatic gas stoves. In this application a manually setcontrol member is employed to hold the gas valve in open position and,in certain stoves, to also hold the oven vent flaps in open position. Acontrolling element is provided to lock the control member in the set oron position. The control member may be either manually or automaticallytripped or released to the off position.

With particular reference to control mechanisms of this general typethat have been known heretofore, the present invention provides a numberof improved and advantageous features. First, the component parts may bealmost exclusively formed by comparatively inexpensive press operations.Additionally, the mechanism is small and compact in size and regular inshape :so that it is easily adaptable to a variety of applications andlocations. Furthermore, by virtue of a novel locking connection betweenthe controlled and controlling members, permissible dimensionaltolerances have been appreciably expanded so that there is no need forcostly hand fitting and finishing on each unit to enable it to givesatisfactory performance.

plied to the controlling element it provides a look which is incapableof disconnection by the load. Furthermore, the load provides a componentwhich assists in unlocking so that when it.

is desired to unlatch very little torque is required. .As a furtherfeature of importance, independent and noninterfering manual andautomatic means are provided for releasing the controlled member. Manualactuating means for the controlling member is provided which is positivein its action so that there is no possibility that it will beineffective to actuate. Resilient means serve to maintain the actuatingmeans in a predetermined on position when the controlled memher islocked. In certain applications it may be convenient to use thecontrolled element as a cam and in these cases the invention providescam follower which desirably is arranged to panying drawings in which:

Figural a front elevation of themechanism,

This connection is also of such a nature that when properly ap- 2 withparts removed, in the off or unlocked position;

Fig. 2 is a front elevation of the mechanism, with parts removed, in theon or locked position;

Fig. 3 is a plan view of the mechanism;

Fig. 4 is a section taken on line 4-4 of Fig. 1; and

Fig. 5 is a rear view of the timer mechanism showing a novel dog legconnection between the timer and the tripping elements; and

Fig. 6 is a diagrammatic view of the locking connection between the searsurface andlocking The improved control mechanism is supported by asuitable frame which may comprise a back mounting plate I anda frontmounting plate 3 spaced from the back plate but having rearwardlyextending side arms '5 formed therefrom which are suitably secured tothe back plate I, as shown at 1. The control mechanism and the actuatingelements therefor are supported by and between the plates l and 3, thusforming a compact and easily mountable assembly. The mechanism 9, shownin the left half of Figs. 1, 2 and 3, comprises the operating mechanismand manual means for actuating the same while the mechanism H appearingin the right half of these figures comprises automatic means,specifically a clock mechanism, for actuating the operating mechanismindependently of the manual actuating means.

The central element of the control mechanism is the plate 13 which, tosuit it to the present application, has a. peripheral cam surface l4formed thereon and will thus be referred to hereinafter as a cam plate,though it will be understood that the improved results of the presentinvention are not dependent upon the specific use of the plate l3. Ashaft [5 is journaled in the back and front plates I and 3 and extendsout-side of the front plate where it has secured thereto the knob 1'! sothat it may be manually rotated. The cam plate l3 ismounted on the shafti5 for rotation relative thereto but its axial position thereon is fixedby suitable means. For this latter purpose, the cam plate l3 may bestaked upon a hub or bushing member l9, as'shown best in Fig. 4. The hubI 9 is freely rotatable on the shaft [5 but is restrained from forwardmovement by a clip 2| which fits in'a suitable peripheral groove in theshaft l-5.- The hub I3 is restrained from rearward movement by abutmentwith the actuator plate 23 which is coaxially secured to the shaft l5,as by means of an engaging flat surface 25, and bears on its 3 rear sideagainst a suitable journal boss provided in the back plate I.

The actuator plate 23 is the medium through which the cam plate I3 isrotated manually by knob I? in a clockwise direction. For this purposethe plate 23 is provided with a radial shoulder 21 and this is engagedby a. rearwardly formed ear 29 on the cam plate It. Thus, when the shaftI5 is rotated in a clockwise direction the radial shoulder 21 ofactuator 23 is also rotated in the same direction and drives the camplate ear 29 before it so that the cam plate 13 is rotated from theposition of Fig. '1 to that of Fig. 2.

When the cam plate I3 reaches the position of Fig. 2, it is lockedagainst further rotary movement in either direction by virtue of thelatch plate 3| acting in conjunction with the actuator plate 23. Thelatch plate 3| is pivoted at 33 to a boss 35 extending forwardly fromthe back plate I, the pivot connection 33 being upwardly and sidewardlyspaced from the shaft l5 and the latch plate 3| being slightly forwardof the cam plate l3. The actuator plate 23 and the latch plate 3| havemutually contacting surfaces which, when engaged, cause the plates torotate together about their respective axes. In order to effect unitaryclockwise rotation, the actuator plate 23 has a generally radial arm 31and to the right thereof the latch plate has a rearwardly extending car39 above its pivot point 3 which crosses the rotary path of the arm 31and may therefore be driven before it in a clockwise direction. In orderto effect counterclockwise rotation of the latch plate 3|, the actuator23 is provided with a second radial arm 4| which is on the right of thelatchplate and has a forwardly extending ear 43 that contacts the edgeof an upward extension '45 on the latchplate above the pivot point 33.

As will be more readily evident hereinafter, pivotal movement of thelatch plate 3| serves to engage or disengage its looking or sear surface41 and a forwardly extending pin 49 which is affixed to the cam platel3. The surface 41 is arranged to intersect the locus or circular pathfollowed by pin 49 as the latter is rotated counterclockwise with thecam plate l3. As best indicated in Fig. 6, the sear surface 41 may be inthe form of a circular arc struck from the center 50, this center beingdisplaced slightly on the right or unlatching side of the axis of pivot33. It will be evident that radii to successive points a, b, and c,which the pin 49 contacts as latch 3| is rotated in a counterclockwiseor unlatching direction, decrease in length so that the pin 49 isactually sliding down an inclined surface, this surface being the searsurface '41. The angle included between the radius and the normal toeach point of contact corres'ponds to the wedge angle of the inclinedsurface. The wedge angle, of course, must be sufliciently low .so thatfrictional forces hold the pin on the surface. On the other hand itprovides means whereby the force of the load applied to cam plate l3assists in 'u'nlatching so that only very small torque applied to plate3| is required to overcome it and unlock the surfaces. The magnitude ofthis torque and its constancy or variation at different contactpositions a, b, c is dependent upon the value of the wedge angle, thetorque increasing as the wedge angle decreases. Instead of a simplecircular arc, a

compound are, or a fiat surface may be employed as the sear surface. Inall cases, however, Where it is desired to take advantage of theassistance the loadon cam plate |3 provides in unlatching, the normalsto the surface 41 should pass to the right of the axis of pivot 33. Thisconstruction centralizes the critical dimensions, 1. e., those definingsurface 41, in one piece, the latch plate 3|, and rather widedimensional tolerances are permissible in the adjoining members, thusproviding a marked saving and facility in manufacturing.

If the operating mechanism is in the position of Fig. L, clockwiserotation of the cam plate I3 alone cannot ordinarily be depended upon toengage the'pin 49 and surface 41 in the manner shown in Fig. 2, andclockwise rotation of the latch plate 3| is desirable to effect thisengagement. This is accomplished by arranging the arm 31 on the actuatorplate 23 so that it contacts the latch plate ear 39 when the pin 49 haspassed the adjacent edge of the surface 41. Clockwise rotation of thearm 31 results in a positive clockwise rotation of the latch plate 3|,and this causes the surface 41 to cross the path or locus of the pin 49behind the pin so that counterclockwise return movement of the pin isblocked by mutual contact of pin and surface. Since no amount ofcounterclockwise torque on cam plate l3 can disengage the pin 49 fromthe surface 41, the latch plate 3| must be rotated in a counterclockwisedirection to effect disengagement. As described above, this may be donemanually by turning the knob H to rotate the shaft l5 and attachedactuator 23 in the counterclockwise direction. When this is done, theactuator ear 43 engages the latch extension 45 to pivot the latch plate3| and unlock the cam plate l3. Counterclockwise rotation of the latchplate 3| to unlock the pin 49 of the cam plate l3 may also be effectedautomatically, as will be presently described. It should be noted againthat an important advantage of the wedgerounded surface lockingconnection between the latch plate 3| and pin 49 on cam plate l3 residesin the ease with which the connection may be broken. The pin 49 isliterally sliding down the incline of the surface 41 and onlyinsignificant torque on latch plate 3| is required to overcome thefrictional contact which looks the pin and surface together.

If desired, the head 5| of the pin 49 may be enlarged and provided witha groove to receive one of a torsion spring 53. The spring 53 surroundsthe shaft l5 and its other end is inserted in a hole 55 therein, the endconnections of the spring being made so that it has initial set orstress. When the shaft I5 is rotated in a counterclockwise direction,the Stress on the spring is increased until the car 43 reaches the latchextension 45 and then upon disengagement of the pin and surface 41forces the cam plate 13, which is freely rotatable on the shaft iii, torotate in a counterclockwise direction until its ear 2.9 strikesactuator shoulder 21, as shown in Fig. 1.

An important function of the spring 53 is to yieldably hold the shaft I5and thus the knob H in a predetermined position so long as the cam plate|3 is locked to the latch plate 3|. Thus, if the actuator plate 23 isrotated an insufficient amount in a counterclockwise direction todisconnect the latch and cam plates, it, the shaft l5, and knob 11 willbe automatically returned by the spring 53 to the on position of Fig. 2.

The latch plate 3| may also have a pair of aeca'rtt spaced cars 51, and59 formed thereon which are adapted to abut the surface of the hub I9.

- These ears serve as safety elements to prevent In normal operation,the cam plate I3 is forced by the load over rotation of the latch plate3|.

in such a manner that it exerts little or no component to rotate the camplate |3 in the clockwise direction which is the only direction inwhich, ,7

the plate 5 3 is free to rotate, it being held against counterclockwiserotation by abutment of its ear 29 with the shoulder 27 of the actuator23 which member is stopped by abutment of its ear 43 with the latchplate extension 35. However, if the cam plate l3 lags behind the latchplate 3| in counterclockwise rotation, the pin 49 is not available as astop but in this case the ear E'lwill abut the hub Hi toprevent'excessive rotation of the latch plate 3|. The sameconsiderations apply to rotation in the clockwise direction and the ear59 serves to limit such movement of the latch plate 3|. The ear 59 mayalso limit clockwise movement of the pin 49, though ordinarily this isaccomplished by engagement of the actuator shoulder 3'| with the latchplate 3| which is itself locked by abutment of a peripheral edge 62 withthe pin 49.

' The foregoing description has shown how the cam plate I3 may be-lockedin a predetermined position by manually rotating it in a clockwiseplished automatically by the timer mechanism 1 which operatesindependently of and does not interfere with the manual controls justdescribed. The automatic control includes a suitable clock mechanism 63which may be actuated and set by a knob 64. An extension arm 65 iscontrolled by the clock 53 and for this purpose it is pivoted at '65 toa hub arm 66 that is directly connected to and controlled by the clockmechanism 63 by virtue of the pivotal connection 65 which it hastherewith. When the clock 63 is running, the arms 85 and 66 are in thedotted line position of Fig. 5 and locked by the clock mechanism againstmovement to the right in this figure or in a counterclockwise directionwhen viewed from the front of the timer. The arm 63 effectuates movementof the arm 65 to the dotted, cocked position by abutment with a lateralear 63 on the arm 65 and when it is released by the timer mechanism atthe expiration of a predetermined period, spring means to be describedreturns the arms to the uncooked position.

A trip arm 69 is pivotally connected at 61 to the extension arm 65. Theconnection 6'! may include a slot H in the arm 69 to permit adjustmentbut in actual operation there is no movement in the slot. Means areprovided to yieldably bias the arms 65 and 69 in the counterclockwisedirection, and this may include a spring 13 that is anchored at one endto an ear on the trip arm 69 and at the other to a forwardly struck car17 extending from the back mounting plate i. It will be apparent thatwhen the timing mechanism 63 releases the arms 65 and 65, the arm 65 andthe trip arm 69 will move quickly to the left (counterclockwise) underthe influence -holds it there, as shown in Fig. l.

striking the shoulder 85.

of the spring 13. The extent of this movement may be regulated by anadjustable stop 19 on the back of the clock '63 which engages with theside of the arm 65.

The movement by spring 13 of the trip arm 69 which has been justdescribed is employed to rotate the latch plate 3| in a counterclockwiseor unlocking direction. For this purpose, the extreme end portion 8| ofthe trip arm 69 is somewhat narrower than the adjacent inner portion 83so as to provide a shoulder 85 which separates these portions and issubstantially normal to the underside surfaces thereof. The latch plate3| has a'forwardly extending ear 8'! formed on its upward extension 45which lies in the path of movement of the shoulder 85 so that when en- Igaged thereby the trip arm 69 will force counterclockwise rotation ofthe latch plate.

A further connection is provided between the trip arm 69 and the latchplate 3| so that the relative movement therebetween may take placefreely-under all condition except the one just described, viz., latchplate 3| in its extreme clockwise position and trip arm 69 movingleftwardly. This connection therefore prevents interference duringmanual locking of the control mechanism 9. It includes an'upwardlyextending web 89 that is connected to, but laterally spaced from, thelatch plate extension 45 by a web 9|. The Web 89 has a guide slot 93through which the triparm 69 extends/and that serves to limit upward andlateral movement of the trip arm. The'lower end of the web is rebent andinclined upwardly to the right to provide a support ear 95 that engagesthe underside of the trip arm 69 when the latch plate 3| is incounterclockwisemost range of its movement. When the operating mechanism9-is cocked and the timer mechanism set, as in Fig. 2, the undersurfaceof the trip arm portion lies on the latch plate ear 8? and the trippingshoulder 85 is spaced slightly from the ear. Afterthe clock 63 releasesthe arm, the shoulder 85 strikes the ear 81 so that the operatingmechanism is unlocked by counterclockwise rotation of the latch plate3|. This movement of the latch plate 3| causes the support car 95 torise and it engages the underside of the trip arm and lifts the shoulder85 over the ear 81 and It will be evident that subsequent clockwisemovement of the latch plate 3| will occur freely, since there is nopossibility of interference due to the ear 8? It will also be evidentthat in the event the operating mechanism 9 is locked but the timermechanism i is not used, so that counterclockwise rotation of the latchplate 3i under manual force is desired, there is also no possibility ofinterference. In this case, the trip arm remains in the position of Fig.l and the latch plate ear 81 rotates underneath the trip arm portion 83so that the shoulder 85 is elevated above a position of possibleinterfering contact with the ear 81.

As already indicated, the cam plate It can be adapted to control avariety of devices and it is not intended to limit the invention in thatrespect. It is often possible to make the connections between thedevices and the cam plate i3 in such a manner thatthey exert acounterclockwise torque on the plate H which is in itself sufficient todrive the cam plate, when unlocked,-

formed on the cam plate. tion includes a-cam follower H1 which comprisesan elongated channel member I09 that is pivotally mounted at a pointintermediate its ends to 31 213051] H that extends between the front andrear plates 3 and I. A tension spring H3 is attached to the right end ofthe member I09 and is anchored to the rear plate I so that it tends torotate the cam follower in a clockwise direction. The other .end of themember rotatably carries a roller 1 l5 that engages the cam surface M tothe right of the mid plane of cam plate :3 so that the force of springH3 not only holds the roller in contact with the cam surface, but alsotends to rotate the cam plate in a counterclockwise direction. The camfollower Nil may on its underside engage the plunger l i! of a valve H79and depress the same to permit flow through fluid lines i2'l and I23when the cam plate is in the locked position of Fig. 2.

In operation, the control mechanism is in the off position when theparts are arranged as shown in Fig. 1. It is set or cocked by manualclockwise rotation of the knob IT. This torque is transmitted to theactuator 23 through the operating shaft !5. The actuator shoulder ii isin engagement with the ear 29 of the controlled member or cam plate [3so that the latter is rotated on the shaft l5 despite the fact that itis .journaled thereon through the medium of the hub 19. It will berecognized that the coaxial arrangement of shaft 15, actuator 23, andcam plate 13 serves to minimize the space required by the mechanism andprovide a compact working assembly.

The cam plate 13 carries a lock element in the form of pin 49 which uponcocking movement may ride on the periphery 6| of the latch 3i and tendto rotate it in the counterclockwise direction. However, latch 3! ispositively rotated in the cleckwise direction by the actuator arm 3?which engages the latch ear 3% after the pin passes the wedge-like orinclined sear surface 47 to force this surface to cross the locus of thepin 49. Clockwise rotation of the cam plate I3 (and of shaft i5) islimited by this clockwise rotation of the latch plate 3! which forcesthe surface 52 against the pin 49, any overrotation of the latch plate3! being prevented by abutment of the ear 59 with the hub E9. The pin 59is therefore confined so that neither clockwise nor counterclockwisetorque on the cam plate is will free it from the latch plate 3!. Thus,in the position of Fig. 2, the control mechanism is in the on or setposition. While, as indicated, clockwise rotation of the shaft is andknob I! is blocked, counterclockwise rotation thereof is, of course, notblocked. It takes place, however, against the resistance of spring 53 sothat if it is insufficient to disconnect the cam plate 13 and latchplate '31, the spring will return the shaft and knob to thepredetermined on position to clearly indicate the condition of themechanism to the user.

The operating mechanism may be tripped or released from its cockedposition of Fig. 2 either manually or automatically. To trip it manuallythe knob I! is rotated in the counterclockwise direction and this torqueis transmitted through the shaft [5 to actuator 23 so that the actuatorcar 43 is moved upwardly against the resistance of spring 53 to engagethe extension 45 of the latch plate 3|. Further rotation of the actuator23 results in counterclockwise rotation of the latch plate 3i and thesear surface 41 is backed The other connecoff thepin 49. From thestandpoint of relative movement, it will be evident-that the pin 49 isin effect moving down the incline of the surface :21, hence for reasonsindicated-above, very little counterclockwise torque need be applied tothe latch plate 3| in order to effect disengagement or tripping of themechanism. At the instant tripping occurs, the knob ll, shaft 15,actuator 23 and latch plate 3| are in substantially their extremecounterclockwise position. When tripping occurs, the cam plate I3 isrotated sharply in the counterclockwise direction by the combined actionof spring 53 and the forces applied by-rod [0i andcam follower i92Excessive overrotation of the latch plate 3 1 before the cam plate Itreaches the position of Fig. 1 is prevented by the ear 5? which may abutthe hub l9, Whereas counterclockwise rotation of the actuator 23, shaftl5, and cam plate I3 is limited by abutment of actuator arm ll with thepost 35. In this manner the mechanism is returned to the predeterminedoff position and is ready for actuation again by clockwise rotation ofthe knob H as just described.

When it is desired to trip the operating mechanism e automatically, theautomatic control mechanism I i may be cocked or set either before orafter the knob I1 is turned to the on.position of Fig. 2. Before thecontrol mechanism ii is set, the under-surface of portion 83 of its triparm 69 rests on the latch ear and if the mechanism l l is not set, thearm 69 remains supported on ear Bl through the cycle of manual operation that has just been described. There is, therefore, no danger ofits interference with the movements of the latch plate 3!. When anautomatic control mechanism H such as the timer mechanism 63 isemployed, the knob 64 is suitably actuated to rotate the arms 65 and 66to the right until the arm 65 is locked in position by the arm 66. Thearm 55 carries the trip arm 69 rightwardly with it so that theundersurface of the trip arm portion 83 drops from the ear 8? to put theshoulder 85 in operative alignment therewith. When the timer mechanismreleases the arm 55, the spring it pulls the trip arm 69 to the left sothat the shoulder 85 strikes the ear 8? to rotate the latch plate 3? inthe counterclockwise direction and effectuate tripping. In its leftwardmovement after tripping the underside of portion 33 of the arm 69 isengaged by the latch car and as the latch 31 is rotated this car liftsthe arm 69 so that the underside of portion 83 is in a position ofnoninterference with further movements of the latch plate 3i From theforegoing description many of the advantageous mechanical features ofoperation of the improved control mechanism will be apparent to those inthe art. When considered from the standpoint of manufacturing andapplication, the device has further advantages. It will be recognizedfor example, that most of the parts can be formed by press operationsfrom sheet metal and that they may be rather easily assem bled.Furthermore, the novel wedge-shaped sear surface t! centralizes all thecritical dimensions in one piece, the latch 3 I, and makes itunnecessary to maintain exacting dimensional tolerances in manufactureand assembly of the other parts. This is demonstrated in Fig. 6, whichshows that for a circular sear surface d'i variations in the distancesbetween pivots 33 and is resulting in variations a, b, and c in thepoints of contact do not appreciably affect the angle between the normalto the point of contact and the radius from pivot 33 to the point ofcontact. However, despite relaxation of dimensional tolerances, thesurface 41 is arranged to provide a positive lock or barrier to movementof the pin 49. The mechanism as a whole is small and compact and regularin shape so that it can be attached to many devices without appreciablealteration or waste space,

Other advantages and features of the invention as well as modificationsthereof will appear upon further consideration, hence it is not intendedto limit the invention to the specific construction described.

What is claimed is:

1. In a control mechanism of the type described, the combination of apivotal controlled member having a rounded surface, a controlling memberpivoted about an axis spaced from that of the controlled member andhaving an inclined surface capable of frictional locking engagement withthe rounded surface, said members being arranged so that when thesurfaces are engaged counterclockwise torque on the controlled membertends to overcome the frictional engagement between the members, anactuator for pivoting the controlled member in a clockwise direction toengage the surfaces and for pivoting the controlling member in acounterclockwise direction to disengage the surfaces, and resilientmeans for holding the actuator in a predetermined position when thesurfaces are engaged.

2. In a control mechanism of the type described, the combination of arotatable controlled member having a lock element thereon, a rotatablecontrolling member having a sear surface thereon coactive with theelement to prevent counterclockwise rotation of the controlled memher,an operating shaft, an actuator coaxially and operably secured to theshaft for rotating the members in the clockwise direction to effectlocking engagement and for rotating the controlling member in thecounterclockwise direction to effect disengagement, and spring meansbetween the controlled member and the shaft energized bycounterclockwise rotation of the shaft when the members are locked andeifective to return the shaft to a predetermined position in the eventcounterclockwise rotation does not effect disengagement of the members.

3. In a control mechanism of the type described, the combination of amovable controlled member, a movable controlling member adapted to lockthe controlled member in a predetermined position, means wherebypredetermined movement of the controlling member releases the controlledmember, manual means for moving the members to effect locking andunlocking, and second means operative without interference with themanual means for also moving the controlling member to release or unlockthe controlled member, comprising a trip member having a predetermineduncocked position, automatically releasable lock means for holding thetrip member in a cocked position, one-way abutment means on the tripmember operatively engageable with the controlling member as the 10 tripmember moves from the cocked position to the one position, and ashoulder slidably engageable with the trip member in said uncookedposition to hold the abutment away from a position of interference withthe controlling member.

4. The invention as ciaimed in claim 3 wherein an ear on the controllingmember provides the last mentioned shoulder.

5. The invention as claimed in claim 4 wherein the abutment contacts theear to cause release movement of the controlling member.

6. In a control mechanism, the combination of a pivotal controlledmember having a latch pin thereon, a pivotal controlling member having asear surface engageable with the pin and disengageable upon rotation ina counterclockwise direction, said surface being formed on an are havinga center spaced on the disengaging side of the controlling members axis,the radii of said pin and surface to a point of mutual contact being insummation greater than the distance between the members axes whereby thesear blocks movement of the pin, an operating shaft, said con trolledmember bein journaled on said shaft, an actuator coaxially secured tothe shaft for rotation therewith, said actuator having an ear forengaging the controlled member to rotate it in a clockwise direction andangularly spaced ears for engaging the controlling member to rotate itin either direction, a torsion spring anchored to a the shaft and to thecontrolled member to yieldably resist relative rotation of the shaft andcontrolled member, stop means for limiting rotation of the controllingmember in either direction, a trip arm having a shoulder thereon,resilient means biasing the arm to the uncooked position, anautomatically releasable lock for holding the arm in cocked position,said controlling member having an ear lyin in the path of uncockingmovement of the arm and engageable by the shoulder when the pin andsurface are engaged so that said arm applies counterclockwise torque tothe member to disengage the pin and surface, and shoulder means on thecontrolling member slidably engageable with the trip arm when the arm isin uncooked position to continuously hold the arm shoulder away frompossible interfering engagement with the ear.

KENNETH M. KIEL.

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